As a known precoating type thread-locking adhesive to be applied to the spirally engaged surface (thread) of a spiral engaging member such as a screw, a bolt and a nut, there has been heretofore known a composition composed of: an organic solvent or water as a solvent; microcapsules containing a reactive adhesive; and a binder resin, as disclosed in JP-B-52-46339 (The term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-2-308876 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-53-11883. Further, JP-A-57-192476 discloses, as a thread-locking adhesive, an adhesive composition composed of: a polymerizable monomer; microcapsules containing a polymerization initiator; a polymerization accelerator; and an aqueous binder of an ethylene/maleic anhydride copolymer. Moreover, JP-A-7-331187 discloses, as a thread-locking adhesive, an adhesive composition composed of: a polymerizable monomer; water-resistant microcapsules containing a polymerization initiator; a polymerization accelerator; and an aqueous binder of an water-soluble polyacetal resin.
Since the precoating type adhesive compositions disclosed in these references are generally in a liquid state, the following procedure is necessary to form an adhesive layer on the spirally engaged surface of a bolt or the like:
(1) a step of applying a liquid precoating type adhesive composition to the surface of an adherend such as a bolt; and PA0 (2) a step of drying the precoating type adhesive composition thus applied, to form an apparently solid layer.
The application of a precoating type adhesive composition in the step (1) has been heretofore accomplished, for example, by spray-coating a liquid precoating type adhesive composition onto an adherend, by dipping an adherend in a liquid precoating type adhesive composition to coat the adherend with the adhesive composition, or by using a coating apparatus as described in JP-B-U-2-43504 (The term "JP-B-U" as used herein means an "eexamined Japanese utility model publication") and JP-B-U-63-4532. Further, as for the step (2), it has been a common practice to allow the coated adherend to stand at ordinary temperature so that it is naturally dried, or to heat the coated adherend to an extent such that the polymerizable adhesive does not undergo a reaction, to thereby accelerate drying.
However, among the microcapsule type adhesives which have heretofore been known, those containing a reactive agent and a reactive initiator (hardener) which are respectively microcapsulized or either of which is microcapsulized are disadvantageous in that the use of a large amount of microcapsules increases a production cost, although they exhibit an excellent storage stability as a liquid adhesive as pointed out in JP-A-7-331187. Further, since the amount of microcapsules, i.e., the amount of the reactive agent used is limited, the resulting adhesion is inadequate.
Among the microcapsule type adhesives containing a water-soluble binder, those containing an aqueous binder which readily becomes water-soluble are disadvantageous in that they require much time to dry after being applied to a bolt or the like. This reduces the productivity. In order to eliminate these difficulties, a precoating type adhesive composition is emulsified by selecting an aqueous binder which exhibits an appropriate water solubility, and thus emulsified adhesive composition is applied to an adherend, to thereby improve the drying property as disclosed in the above mentioned JP-A-5-140514. However, such a precoating type adhesive composition has a high viscosity in a liquid form and thus is disadvantageous in that it is difficult to control the amount thereof to be attached to an adherend in the case where the application is conducted by dipping the adherend in the adhesive composition. Thus, if a diluent is added to the precoating type adhesive composition to adjust the viscosity thereof, it causes problems such as a drop of adhesion, which is one of the originally intended properties of the precoating type adhesive composition. Further, although this emulsified solution of the precoating type adhesive composition forms a solid surface layer fast, water content thereof tends to remain inside as drying at the surface thereof proceeds. This requires much time for the film to dry. Moreover, a shrinkage of the formed layer accompanied with the drying produces voids inside the formed layer or deteriorates the external appearance of the formed layer.
Further, the above mentioned JP-A-57-192476 discloses, as a thread-locking adhesive, an adhesive composition composed of: a polymerizable monomer; microcapsules containing a polymerization initiator; a polymerization accelerator; and an aqueous binder of an ethylene/maleic anhydride copolymer. However, this composition also forms an emulsion state liquid matter similar to the above composition. Therefore, the water content thereof tends to remain inside the resulting solid surface layer. Moreover, there may be cases where the storage stability of the emulsified liquid comnposition itself is deteriorated, or where the reactive substance in the dried coating layer is denatured to deteriorate the adhesion.